A. L. Dawar

Effect of uv exposure on optical properties of amorphous as(2)s(3) thin films.

Systematic studies of the refractive index, extinction coefficient, and optical band gap have been made of as grown and UV-exposed amorphous films of As(2)S(3) grown by thermal evaporation from resistive source. The refractive index and extinction coefficient have been found to change with different UV exposure duration. No noticeable change was observed in the optical band gap with UV exposure.

Electrical properties of Te-rich, Cd-rich and hydrogen-exposed polycrystalline CdTe thin films

Polycrystalline films of CdTe, stoichiometric, Te-rich, and Cd-rich, were grown using a vacuum evaporation technique on glass substrates kept at room temperature. The as-grown films were exposed to hydrogen gas at high pressure (200-500 PSI). Measurements of DC conductivity in the temperature range 77-300K, X-ray diffraction studies and electron probe microanalyses were made on these films. The conductivity data for the stoichiometric, Te-rich and Cd-rich films in the low temperature region have been analysed for variable range hopping conduction on the basis of Motts model. The analysis of the high temperature conductivity data for Te-rich and hydrogen-exposed films has been based on Setos model of thermionic emission. It is found that addition of Te and Cd improves the conductivity of the films by four and six orders of magnitude respectively. However, the density of trap states near the Fermi level, N(EF), also increases with increase of Cd and Te content. In the case of hydrogen-exposed films the conductivity decreases with increase of gas pressure.

Effect of laser irradiation on structural, electrical and optical properties of SnO2 films

Thin films of SnO2 were prepared using a spray pyrolysis technique. Films were irradiated with Nd:YAG laser pulses of various energy densities (2–50 mJ cm−2) with varying number of pulses from 1–50. X-ray diffraction studies were made to investigate the structural changes due to laser irradiation. An improvement in crystallinity and an increase in grain size were observed in laser-irradiated films. Hall coefficient and Hall mobility studies were made in the temperature range 77–300 K for the as-grown as well as laser-irradiated films. An increase in mobility and a decrease in carrier concentration were observed in the films after laser irradiation. Optical transmission studies revealed that the refractive index increased as a result of laser irradiation.

Effect of laser annealing on the structural, electrical and optical properties of CdTe thin films

Abstract CdTe films of 0.7 μm thickness were deposited by a resistive heating onto glass and KBr substrates kept at 200°C. The films were irradiated with laser pulses of various energy densities. A pulsed lase (Nd: YAG) capable of producing 20 ns pulses of wavelength 1.06 μm with varying energy densities (2–50 mJ/cm2) was employed. The films were examined by TEM and X-ray diffraction and found to be polycrystalline. DC conductivity and Hall coefficient measurements were made on the films in the temperature range 77–400 K. The optical energy gap has been calculated using the optical transmission spectra.

Effect of laser irradiation on structural, electrical, and optical properties of p-mercury cadmium telluride

Single crystals of p‐Hc1−xCdxTe (x=0.16) were grown by the Bridgeman technique. The bulk single crystals were irradiated with laser pulse of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53 μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the Van der Pauw technique in the temperature range 77–300 K for both as‐grown and laser‐irradiated samples. Also the x‐ray diffraction pattern and transmission measurements of the samples were taken at room temperature. Electrical studies shows that the p‐mercury cadmium telluride after the laser irradiation becomes n type and optical results show that the free‐carrier concentration after laser irradiation increases sharply so that there is negligibly small transmission. The x‐ray studies show that single crystal p‐type samples after laser irradiation undergo structural changes as well, introducing ...

Effect of laser annealing on electrical and optical properties of n‐mercury cadmium telluride

Single crystals of n‐Hg1−xCdxTe (x=0.18) were grown by the Bridgman technique. The bulk single crystals were irradiated with laser pulses of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53‐μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the van der Pauw technique in the temperature range 77–300 K, for both as‐grown and laser‐irradiated samples. Also, transmission measurements of the samples were taken at room temperature. Both electrical and optical studies showed that laser irradiation introduces additional defects in mercury cadmium telluride (MCT), and its quality deteriorates instead of improving as observed in many other semiconductor materials. We found that laser irradiation increases free‐carrier concentration and decreases the band gap of MCT.

The effect of a non-stoichiometric excess of tin on the electrical transport properties of epitaxial p-type type SnTe thin films

Abstract The electrical transport properties (the d.c. conductivity, the Hall coefficient and the Hall mobility) of epitaxial p-type SnTe films were measured in the temperature range 100–500 K for various non-stoichiometric excesses of tin. It was concluded from the experimental data that excess tin decreases the number of tin vacancies, thereby decreasing the concentration of free holes and increasing their mobility. The results are discussed in terms of a model involving two valence bands.

Electrical transport properties of copper-doped tellurium films

Abstract Polycrystalline films of copper-doped tellurium were grown by co-evaporating copper and tellurium from separate boats. Measurements were made of the electrical transport properties of these films. It was observed that the addition of copper decreases the activation energies of both the conductivity and the mobility. The low temperature conduction data were interpreted on the basis of a variable range hopping mechanism while the high temperature data indicate the dominance of the grain boundary scattering mechanism.

Fabrication of low resistive CdS thin films

Abstract Low resistive and high mobility thin films of CdS have been grown using vacuum evaporation techniques. X-ray diffraction studies show that the films are well oriented with a preferential growth of crystallites in the (002) plane. The value of conductivity observed in these films is in the range 0.088Ω -1 cm -1 −1.34Ω -1 cm -1 at 300 K.

Effect of hydrogen annealing on structural and optical properties of ZnSe thin films

Abstract ZnSe thin films grown by vacuum evaporation were annealed in hydrogen atmosphere for a duration of 30 min at different temperatures in the range 200–350°C. X-ray diffraction and optical transmission studies were made on these films. Refractive index and extinction coefficient have been estimated for the wavelength region (0.6–2.0 μm) for as-grown and hydrogen annealed films. The values of refractive index and extinction coefficient have been found to decrease with the increase of annealing temperatures. The crystallinity and grain size of films is found to increase.